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What kind of meter is used to find output of LED driver

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domelectric

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Location
Sarasota, Florida
I was testing the output of an led driver and my fluke multimeter read zero volts, however a known working lamp lit up. I guess I'm using the wrong test equipment and my boss got on me for wasting a trip by not having the right meter. He said I need to use an analog meter like a Simpson. I would like to find a DMM. Any suggestions. BTW, the reason I needed to know the output voltage was because the LED manufacturer wanted to know the exact output for warranty reasons. Thank you.
 
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__dan

Senior Member
Have not tried measuring that myself but the LED driver is a regulated constant current source, not a constant voltage source. The LED load is a diode, essentially a short if the voltage is in the forward bias direction. The forward bias voltage drop could be very low, maybe below 1 volt DC, which the T1000 reads as zero (guessing at this point).

So if the LED array is rated 1000 mA, the driver would be rated 1000 mA output current regulated, not rated by its output voltage.

Essentially, the LED load and the driver are matched combinations, matched by regulated constant current, and that number will change with different LED loads. Other numbers like open circuit voltage, voltage under load, are probably not even listed in the documentation, but the manufacturer will know those.

I would suspect if the manufacturer wants an exact reading of the driver's output, they would want the current flow under load. I would inquire with the manufacturer to clarify this, then current flow can be measured with many DMM's in series in the circuit.
 
sparkyrick

sparkyrick

Senior Member
Location
Appleton, Wi
I've run across this same problem with puck light drivers. The output voltage isn't DC, but a high frequency AC voltage, not the usual 60Hz and my Fluke couldn't read it either. I even tried it on a working set of puck lights on AC and DC, no go. Then, in small print on the driver, it stated that the output couldn't be read by typical test equipment. Dumb.
 
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big john

Senior Member
Location
Portland, ME
__dan said:
Have not tried measuring that myself but the LED driver is a regulated constant current source, not a constant voltage source. The LED load is a diode, essentially a short if the voltage is in the forward bias direction. The forward bias voltage drop could be very low, maybe below 1 volt DC, which the T1000 reads as zero (guessing at this point)...
Click to expand...
Many fixtures are composed of groups of series connected LEDs that would have a pretty significant combined voltage drop when forward biased. I can't say the driver has no current-limiting ability, but it would be unnecessary once the LEDs are lit: With steady DC they would act like a normal resistive load.

That said, if the drivers are supply PWM power for dimming or if there's some sort of initial impedance change during lighting, then I agree it might be much more difficult to accurately measure.

But in that case does the manufacturer list an OCV that should be present when the lamp is disconnected? That's true of many fluorescent fixtures.
 
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mgookin

mgookin

Senior Member
Location
Fort Myers, FL
Occupation
Retired inspector, plans examiner & building official
domelectric said:
I was testing the output of an led driver and my fluke multimeter read zero volts, however a known working lamp lit up. I guess I'm using the wrong test equipment and my boss got on me for wasting a trip by not having the right meter. He said I need to use an analog meter like a Simpson. I would like to find a DMM. Any suggestions. BTW, the reason I needed to know the output voltage was because the LED manufacturer wanted to know the exact output for warranty reasons. Thank you.
Click to expand...

Do you have a model number/ part number for the LED's?
Have you read the spec sheet?
If those don't answer your question, the manufacturer should be able to tell you what you're looking for and what meter to use.
There are many products coming to market seemingly every day.

What's the problem with the lights which you are diagnosing?

As to your boss, well, he's the boss.
 
T

The Spunkster

Member
Location
South Jersey,USA
Occupation
NJ Lic. Electrical Contractor /1995 to present
Today's electrician as a troubleshooter needs a inexpensive portable single trace scope. Than you can read ACtoDC and any where between them. Good Luck!
 
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canoeman

Member
Location
United States los angeles california
Measuring pwm led drivers.

Measuring pwm led drivers.

[The only way to measure the PWM ( pulse width modulation) is with an ocilliscope. Pulse width modulation is switched dc . a regular digital scope, or a fluke scope will work fine. Go to adafruit.com, to see how to measure pwm switching power supplies for leds

The measurement on the digital scope will show time interval between pulses, and the voltage level.



QUOTE=big john;1696237]Many fixtures are composed of groups of series connected LEDs that would have a pretty significant combined voltage drop when forward biased. I can't say the driver has no current-limiting ability, but it would be unnecessary once the LEDs are lit: With steady DC they would act like a normal resistive load.

That said, if the drivers are supply PWM power for dimming or if there's some sort of initial impedance change during lighting, then I agree it might be much more difficult to accurately measure.

But in that case does the manufacturer list an OCV that should be present when the lamp is disconnected? That's true of many fluorescent fixtures.[/QUOTE]
 
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